1. Forces and Changes in Movement
17 November 2018 Objectives: To describe the relationship between forces, mass and acceleration.

2. Starter (5 mins)
Show the students a video clip of a fairground catapult that launches people into the air, for example:
Ask them to describe the motion and the forces acting just before and after the capsule launches.

3. Balanced and unbalanced forces
Imagine a car travelling at a constant speed of 50 km/h.
The engine provides sufficient force to balance all the frictional forces that are acting to decrease the speed.
500 N
500 N

4. Balanced and unbalanced forces
A crosswind acting on the car produces a sideways force.
500 N
500 N
100 N
cross wind
The crosswind causes the direction of the car to change – this happens because the sideways forces on the car are not balanced. The car will veer sideways.
If the car turns right so that the wind is now behind the car, what will happen to the speed?

5. Resultant force
The sum effect of more than one force is called the resultant force.
The resultant force is calculated by working out the difference between opposing forces in each direction.
What is the resultant force on this truck?
A resultant force of 100 N is accelerating the truck.
400 N
500 N

6. Balanced and unbalanced forces – summary
If the forces on an object are balanced:
and the object is stationary, it will remain stationary
and the object is moving, it will continue to move at the same speed and in a straight line.
In other words, the object will continue to do what it is already doing without any change.
If the forces are unbalanced, two things can happen:
The speed can change. This is called acceleration.
The direction of motion can change.

7. Balanced and unbalanced forces – summary
If the forces on an object are balanced:
and the object is stationary, it will remain stationary
and the object is moving, it will continue to move at the same speed and in a straight line.
In other words, the object will continue to do what it is already doing without any change.
If the forces are unbalanced, two things can happen:
The speed can change. This is called acceleration.
The direction of motion can change.

8. Practicals
There are two possible relationships to investigate. These are initially investigated by exploring two separate hypotheses, each covered by a separate worksheet. The hypotheses are:
The greater the force, the greater the acceleration for a fixed mass.
The greater the mass, the less acceleration there will be for a fixed force.
See practical sheets

9. Plenary
Pupil assessment and feedback sheet (next steps sheet)